定义一个可比较的类

[b]Defining a comparable type[/b]

public class Date implements Comparable<Date> {
	private final int day;
	private final int month;
	private final int year;

	public Date(int d, int m, int y) {
		day = d;
		month = m;
		year = y;
	}

	public int day() {
		return day;
	}

	public int month() {
		return month;
	}

	public int year() {
		return year;
	}

	public int compareTo(Date that) {
		if (this.year > that.year)
			return +1;
		if (this.year < that.year)
			return -1;
		if (this.month > that.month)
			return +1;
		if (this.month < that.month)
			return -1;
		if (this.day > that.day)
			return +1;
		if (this.day < that.day)
			return -1;
		return 0;
	}

	public String toString() {
		return month + "/" + day + "/" + year;
	}
}